Shabbos 86 – שבת פו

According to Rebbi Akiva, five complete onas are required, to be completed with the sixth when missing part of the fifth. In this case, the sixth will inevitably be of a different nature than the fifth (one day the other night) with a different length. How can one compensate for the other?

Meraimar responded that there was actually no Tvul Yom present at receiving the Torah. Can this be proven from a source, or was it known from tradition?